This invention relates generally to fluid control valves provided with positive and negative load compensation.
In more particular aspects this invention relates to pressure compensated direction and flow control valves, the positive and negative load compensators of which are controlled by a single amplifying pilot valve stage.
In still more particular aspects this invention relates to pilot operated pressure compensated controls of direction control valves, used in control of positive and negative load, which permit variation in the level of control differential across metering orifices of the valve spool, while this control differential is automatically maintained constant at each controlled level.
In still more particular aspects this invention relates to pilot operated pressure compensated controls of direction control valves, which provide a priority feature for specific valves by controlling the pressure differential of all of the nonpriority valves.
Closed center fluid control valves, pressure compensated for control of positive and negative loads, are desirable for a number of reasons. They permit load control with reduced power losses and therefore, increased system efficiency. They also permit simultaneous proportional control of multiple positive and negative loads. Such fluid control valves are shown in my U.S. Pat. Nos. 4,180,098, issued Dec. 5, 1979 and also in my 4,222,409 issued Sept. 16, 1980. However, the valves of those patents although capable of proportional control of positive and negative loads, use for such control the energy directly transmitted through the load pressure sensing ports, which not only attenuate the control signals, but limit the response of the control. Those valves also automatically maintain a constant pressure differential across metering orifices in control of both positive and negative loads. In those valves the priority feature is obtained by throttling the fluid flow to the down stream valves, so that the priority valve is always assured to the required flow, once the maximum flow output of the system pump is reached. Also in those valves the construction of the priority valve is substantially different from the nonpriority valves and the priority valve must work in a series type circuit.